[issue8299] Improve GIL in 2.7

[Antoine Pitrou]

Antoine Pitrou <pitrou at free.fr> added the comment:

> The counter is "stall cycles".
> During the 10 second run on my 2.4Ghz cpu, we had instruction cache
> miss stalls for 2 billion cycles (2000 samples of 1000000 cycles per
> sample).  That does account for around 10% of the availible cpu.

Ok, thanks.

> 2) The poor performance of competing CPU threads on multicore machines
> is due to the instruction cache behaviour of non-overlapping thread
> execution on different cores.

Have you tried your measurement approach with ccbench?

> We can fix 1) easily, even with a much less invasive patch than the
> ones I have put in here.  I'm a bit surprised at the apparent
> disinterest in such an obvious bug / fix.

As already said, it's too late for 2.7. And the fix in 3.2 is most
probably better.

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